#include<stdio.h>
int main()
{
	int n;
    scanf("%d",&n);
	while(n)
	{
		double sum= 0,s;
		for(int i = 1;i<=n;i++)
		{
			if(i==1)
			{
				sum+=n;
			} else{
			   s = (1.0/i)*(n-i+1);
			   sum = sum+s*2;
		    }
		}
		printf("%.2f\n",sum);
		scanf("%d",&n);
	}
}